I have a bootable USB with Ubuntu 16.04. I use it in my mac but every time I reboot, I lose all settings Ive made. (resolution, wifi password, files, etc) What can i do to fix it? Also I cannot access to Macintosh to save files there. Sorry for my english, im from Argentina.
I can't understand you well, but I think that you're trying to say is that you want to make your USB work like an Ubuntu portable installation.
Try to follow this guide, but set the "space used to preserve files across reboots" the space you want to have.
(e.g. if you want to have 1 GB space, put there 1024)
I hope this works.